The invention provides a preparation method of geutianae anti-irritation factor and a plant extraction device. The preparation method comprises the following steps: smashing the medicinal material, namely, herba geutianae, feeding the smashed medicinal material into the plant extraction device, carrying out aqueous extraction, discharging the aqueous extracted solution and medicinal dregs; and adding a solvent, and carrying out thermal desorption under the condition that inert gas exists, thus obtaining the geutianae anti-irritation factor. The plant extraction device comprises a tank, a top cover and a lower opening cover, wherein the top cover and the lower opening cover are arranged on the top and bottom of the tank, and a ceramic film layer and a carbon fiber layer are arranged in the sequence from outside to inside on each of the inner side wall of the tank and the inner side of the lower opening cover. The preparation method and the plant extraction device have the advantages that extraction and adsorption are carried out at the same time, during the extraction process, the active ingredients are timely transferred into the activated carbon fibers, so that a relatively high concentration gradient is always kept between the extracted liquid and medicinal materials, the extracting ratio is high, and meanwhile, the use amount of the solvent is reduced.